Microsurgical instruments can be used by surgeons for removal of tissue from delicate and restricted spaces in the human body, particularly in surgery on the eye, and more particularly in procedures for removal of the crystalline lens or the vitreous body. Such instruments include a control console and a surgical handpiece with which the surgeon dissects and removes the tissue. The handpiece has a surgical tool such as an ultrasonic microsurgical cutter for cutting or fragmenting the tissue and is connected to the control console by a long power cable and by long conduits or flexible tubes for supplying an irrigation fluid to the surgical site and for withdrawing or aspirating fluid and fragmented tissue from the site. The cutting, irrigation and aspiration functions of the handpiece are controlled by the remote control console that not only provides power for the surgical cutter (e.g., an ultrasonically vibrated needle), but also controls the flow of irrigation fluid and provides a source of reduced pressure (relative to atmosphere) for the aspiration of fluid and fragmented tissue. The functions of the console are controlled manually by the surgeon, usually by means of a foot-operated switch.
The multiple connections that are required between the handpiece and the console for the power cable and the suction and irrigation lines have made the preparation and interconnection of the equipment prior to the surgical procedure extremely complex, with the resultant concerns over maintaining the sterility of the equipment and assuring error-free connection. Accordingly, the typical microsurgical instruments, the fluid handling connections have come to be centralized in a “cassette” that contains in one unit all of the connections for the aspiration and irrigation lines, internal conduits for directing the flow of fluids, valves for controlling the flow of fluids into and out of the handpiece, a receptacle for aspirated fluid and tissue, and may contain the tube portion of a peristaltic pump. The cassette typically is supplied in a sterile package with color-coded connecting tubing already attached. Thus, setting up the equipment requires only connecting the cassette tubing to the surgical handpiece and irrigation fluid source and inserting the cassette into a receptacle in the console. The receptacle may contain the roller head portion of a peristaltic pump (or some other access to reduced pressure), an aspiration line pressure sensor and devices for operating the valves in the cassette and for controlling the flow of irrigation or aspiration fluids through the fluid conduits within the cassette. For convenience and to maintain sterility, the cassette may be discarded after a single use or sterilized and reused.
Sensitive instruments such as these microsurgical cassettes can require very accurate calibration in order to function properly. For example, the microsurgical cassettes used to assist with surgical irrigation or suction in eye surgery require highly accurate pressure/displacement calibration curves to accurately determine a given pressure based on a measured diaphragm displacement. Because of the sensitive nature for calibrating such cassettes, and because each cassette can have a slightly different calibration curve, it is advantageous to communicate accurate calibration information specific to each individual cassette to the console with which the cassette will be used. Efficiently communicating calibration information can be difficult, particularly where the calibration curve is highly nonlinear and requires multiple coefficients for a modeling polynomial, or multiple data points for accurately reconstructing the specific calibration curve.
One solution for communicating calibration information is to break typical calibration curves down so as to be categorized into one of a predetermined number of categories. Such a method, however, has the obvious drawback of being unable to accurately reflect calibrations across a broad spectrum. Another method is to communicate the coefficients of a polynomial that models the calibration curve. For example, a fourth order polynomial can be used to model the pressure/deflection calibration curve illustrated in FIG. 3. By sending the coefficients for each term in the fourth order polynomial, the calibration curve can be reconstructed by the console with which the cassette is to be used. However, accurately reproducing a non-linear curve—especially higher order curves—requires communicating very precise coefficients and thus is not well suited for use with a small data space such as a single linear barcode.
Another method is to convey sufficient data points from the calibration curve so that the console can mathematically determine a function modeling the overall curve. For example, if the modeling function is an nth order polynomial, n+1 data points will fully determine the polynomial coefficients. Such a method is made difficult though by the fact that small deviations in the communicated values (due for example to rounding or measurement tolerance) can result in significant error in the calculated modeling function. This is particularly true of highly non-linear systems. Thus, communicating sufficient data points to fully and accurately determine a calibration curve typically requires communicating a large data set to reduce such deviations.
Microsurgical cassettes are often intended to be a single-use disposable or are otherwise produced in bulk quantities. Because the calibration information for each cassette is unique, it is desirable to include the calibration information for each cassette in a convenient form that can accompany the cassette. Traditional methods of providing n+1 data points with sufficient precision to determine a modeling polynomial, or providing sufficiently precise coefficients for an approximating polynomial for each device, can be cumbersome or impractical for use with a limited amount of data, such as a single barcode. What is needed then is a method for conveying accurate calibration data in an efficient and compact manner. Embodiments of the present invention address this problem by presenting systems and methods for compressing and encoding data, such as calibration data, so that it can be communicated in a more succinct and cost-effective manner. According to one embodiment, pressure/displacement calibration data for a disposable microsurgical cassette can be compressed to fit within a single barcode on the disposable cassette. According to other embodiments, other methods for compressing data and for extracting information from compressed data are presented.